Form of Freshwater Codenterate. 113 



a left half. The direct union of this cavity with the axial 

 cavity of the common support takes place through the peduncle 

 of the bud, which diminishes in size at this time. By trans- 

 mitted light the common support, as well as the buds, appears 

 perfectly transparent ; by direct light, as already stated, milky 

 white with a bluish tinge. The cavity of the buds and the 

 stolo is filled with a fluid which coagulates on the applica- 

 tion of reagents. In this phase of development the endo- 

 dermal cells appear in sections distinctly contoured, with a 

 readily recognizable large nucleus ; their protoplasm is 

 transparently granular, and permeated in the part turned 

 towards the bud-cavity by a great number of vacuoles, side 

 by side with which yolk-globules are to be found here and 

 there in small numbers. In the ectoderm, which is in contact 

 with the yolk, on the contrary, all the cells are filled with 

 yolk- globules. The latter are taken up by the ectodermal 

 cells directly and without first breaking up. In the wall of the 

 stolo opposite to the buds, and turned towards the central yolk- 

 nucleus, the ectodermal cells are just as transparent as those 

 of the endoderm and contain no vitelline globules. 



From this it follows that in the vermiform organism 

 parasitic in the ova of the Sterlet and investigated by me, 

 the process of nutrition which is more and more actively 

 carried on during the gradual growth of the primary and 

 secondary buds, is exclusively performed by the ectodermal 

 cells of the buds, the vitellus of the ovum, which is energetically 

 incepted hy the latter, penetrating through the endodermal cells 

 into the hud-cavity, where it collects in the form of reserve 

 nutritive material. 



The development of the buds concludes with their most 

 complete possible separation from one another and with the 

 appearance of tentacles. 



The upper part of the secondary bud, with the above-men- 

 tioned shallow groove, represents the lower aboral end of the 

 future free-living form ; and the furrow running parallel to 

 the long axis itself indicates the direction of the plane of 

 division which in the sequel halves the free-living generation, 

 the ''mothers." 



Twelve previously-forming tentacles, six on each side of 

 the bud, in the neighbourhood of its peduncle, as well as 

 the other twelve secondary tentacles, likewise appearing 

 above, six on each side of the longitudinal groove, are deve- 

 loped with the co-operation of all the three cell-layers of the 

 hud (but especially the mesoderm). They grow from without 

 inwards into the cavity of the bud, in the fashion of intro- 

 verted glove-fingers (fig. 4) . 



Ann. & Mag. N. Hist. Ser. 5. Vol. xviii. 8 



